1. Field of the Invention
The present invention relates to a combustion condition detecting apparatus for an internal combustion engine for detecting combustion a combustion condition, and more particularly to a combustion condition detecting apparatus for an internal combustion engine for detecting combustion conditions such as a knock generating condition or a cylinder discrimination on the basis of an ionic current generated in a cylinder that is immediately after the combustion.
2. Description of the Related Art
Conventionally, there has been proposed an apparatus, in which an ignition plug is used as an electrode for detecting an ionic current, for detecting combustion conditions, for example, for detecting an absence/presence of a knock or for discriminating a combustion cylinder on the basis of an amount of the ionic current detected immediately after the ignition.
The discrimination of the combustion cylinder, i.e., the cylinder discrimination means to identify which cylinder is under combustion in a simultaneous ignition mode immediately after the start of the engine. In a four-cycle internal combustion engine in which the motion of the ignition stroke and the motion of the exhaust stroke are the same, it is possible to detect which cylinder is under combustion stroke if a motion of a cam is physically detected by providing, for example, a sensor such as a cam sensor. However, in the case of, for example, a crank sensor only, without providing such a sensor, it is impossible to know which cylinder is under combustion.
In view of the foregoing fact, in the simultaneous ignition mode immediately after the start of the engine, fuel is injected simultaneously to, for example, two cylinders that are in synchronism with each other in the ignition stroke and the exhaust stroke and ignited. Since the ionic current is detected in the cylinder that is under combustion, the cylinder that is under combustion is identified on the basis of the ionic current.
In the simultaneous ignition mode, the fuel is simultaneously injected and the ignition is simultaneously effected by grouping a plurality of cylinders in which the ignition stroke and the exhaust stroke are performed at the same timing, for example, the first cylinder and the fourth cylinder, and the second cylinder and the third cylinder. Then, after the judgement of the cylinder that is under combustion stroke has been identified on the basis of the ionic current as described above, the operation is moved therefrom to a regular mode in which the fuel is injected in a sequential manner only into the cylinder under ignition stroke and the ignition is effected.
On the other hand, with respect to the detection of absence/presence of the knock, if the knock is generated in the internal combustion engine, a vibratory component of the knock is superimposed on the ionic current. For this reason, by extracting this vibratory component, it is possible to judge whether the knock is generated.
FIG. 3 is a block diagram showing a conventional combustion condition detecting apparatus for an internal combustion engine. In FIG. 3, reference numeral 21 denotes an ignition coil provided for each cylinder for generating an ignition high tension voltage and numeral 10 denotes a power transistor having an emitter thereof grounded. Numeral 20 denotes an ignition plug for discharging by the application of the ignition high tension voltage to ignite the mixture within the cylinder of the internal combustion engine. Numeral 30 denotes an ionic current detection circuit for charging the high tension voltage (bias voltage) for detecting an ionic current 6 by utilizing a secondary voltage of the ignition coil and for detecting as an ionic current detection signal the ion current generated when the discharge for ignition has been completed.
Also, numeral 3 denotes a combustion signal processing circuit composed of a comparator circuit and a timer circuit for producing a combustion signal by comparing with a predetermined detection level the ionic current detection signal outputted from the ionic current detection circuit 30. Numeral 4 denotes a knock signal processing circuit composed of a filter circuit and a waveform shaping circuit for picking up a knock signal, that will become a base for the knock detection, from the ionic current detection signal outputted from the ionic current detection circuit 30, for performing a waveform shaping to output a knock pulse. Numeral 5 denotes an ECU (electronic control unit) for inputting the combustion signal and a knock pulse to discriminate the combustion cylinder and to detect the absence/presence of the knock based upon various signal changes.
As shown in FIG. 3, the ionic current detection circuit 30, the combustion signal processing circuit 3, and the knock signal processing circuit 4 are provided for each cylinder.
In the thus constructed combustion condition detecting apparatus, the combustion conditions such as the discrimination of the combustion cylinder and the detection of absence/presence of the knock are detected on the basis of the ionic current extracted by the ionic current detection circuit 30.
Also, FIG. 4 is a block diagram showing another example of a conventional combustion condition detecting apparatus for an internal combustion engine. In the conventional example shown in FIG. 4, the ionic current detection circuit 30, the combustion signal processing circuit 3 and the knock signal processing circuit 4 are provided commonly for the four cylinders. FIG. 5 is a timing chart showing an output signal of each part of the circuit in FIG. 4. The numerals used in the leading part of the signal names in FIG. 5 correspond to contact points indicated by the same numerals in FIG. 4.
In the thus constructed combustion condition detecting apparatus, since the ionic current detection circuit 30, the combustion signal processing circuit 3 and the knock signal processing circuit 4 are provided commonly for the four cylinders, it is possible to reduce the scale of the circuit.
In the thus constructed conventional combustion condition detecting apparatus, in the conventional example shown in FIG. 3, since the ionic current detection circuit 30, the combustion signal processing circuit 3 and the knock signal processing circuit 4 are provided for each cylinder, there is a problem that the circuit scale is enlarged to increase a cost or a size.
On the other hand, in the conventional example shown in FIG. 4, it is possible to reduce the scale of the circuit. However, for example, in the case of the knock detection, as indicated by the ionic current detection signal indicated by the numeral 7 in FIG. 5, the sum of the ionic current detection signals of the respective cylinders is inputted into the knock signal processing circuit 4. Therefore, there is a fear that the knock detection would be incorrectly performed. In particular, at a high engine rpm, since noise upon the turn-on of the ignition signal of the cylinder that will be ignited next is superimposed on the knock signal of the previous cylinder, there is a problem that it is impossible to discriminate the knock signal from the noise to induce a misjudgment.
The present invention has been made in order to solve the above-noted defects, and therefore has an object to provide a combustion condition detecting apparatus for an internal combustion engine, which may well detect the combustion conditions such as discrimination of a combustion cylinder and detection of absence/presence of a knock and may reduce a circuit scale therefor.
In order to achieve the above object, according to one aspect of the present invention, there is provided a combustion condition detecting apparatus for an internal combustion engine, comprises an ignition coil provided for each cylinder for generating an ignition high tension voltage; an ignition plug for discharging by the application of the ignition high tension voltage to ignite mixture within the cylinder of the internal combustion engine; a bias circuit provided for each cylinder for applying a bias voltage to the ignition plug; an ionic current detection circuit provided for each cylinder for detecting as an ionic current detection signal an ionic current corresponding to an amount of ion generated in the cylinder that is immediately after the combustion of the mixture; a knock signal processing circuit provided one for a combination of a plurality of cylinders that are every two or more cylinders in ignition order to produce a knock signal for representing a knock generation condition of the internal combustion engine on the basis of the sum of the ionic current detection signals; and an ECU for detecting the combustion condition of the ignition plug on the basis of the knock signal and for calculating a control parameter.
According to another aspect of the present invention, there is provided the combustion condition detecting apparatus for an internal combustion engine, further comprising a combustion signal processing circuit provided one for a plurality of cylinders of a combination different from the combination of the cylinders that are under simultaneous ignition in a simultaneous ignition mode and for producing a combustion signal by comparing the sum of the ionic current detection signals with a predetermined detection level, wherein the ECU makes a cylinder discrimination and a combustion judgement on the basis of the combustion signal.
According to still another aspect of the present invention, there is provided the combustion condition detecting apparatus for an internal combustion engine, wherein the ionic current detection circuit is made up of a current mirror circuit for feeding to the combustion signal processing circuit an ionic current detection signal similar to the ionic current detection signal to be fed to the knock signal processing circuit.
According to a further aspect of the present invention, there is provided a combustion condition detecting apparatus for an internal combustion engine, comprises an ignition coil provided for each cylinder for generating an ignition high tension voltage; an ignition plug for discharging by the application of the ignition high tension voltage to ignite mixture within the cylinder of the internal combustion engine; a bias circuit provided for each cylinder for applying a bias voltage to the ignition plug; an ionic current detection circuit provided for each cylinder for detecting as an ionic current detection signal an ionic current corresponding to an amount of ion generated in the cylinder that is immediately after the combustion of the mixture; a combustion signal processing circuit provided one for a plurality of cylinders of a combination different from the combination of the cylinders that are under simultaneous ignition in a simultaneous ignition mode and for producing a combustion signal by comparing the sum of the ionic current detection signals with a predetermined detection level; and an ECU for making a cylinder discrimination and a combustion judgment on the basis of the combustion signal.